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Ben-Gharbia, H., Yahia, O. K. - D., Amzil, Z., Chomerat, N., Abadie, E., Masseret, E., et al. (2016). Toxicity and Growth Assessments of Three Thermophilic Benthic Dinoflagellates (Ostreopsis cf. ovata, Prorocentrum lima and Coolia monotis) Developing in the Southern Mediterranean Basin. Toxins, 8(10), 297.
Résumé: Harmful benthic dinoflagellates, usually developing in tropical areas, are expanding to temperate ecosystems facing water warming. Reports on harmful benthic species are particularly scarce in the Southern Mediterranean Sea. For the first time, three thermophilic benthic dinoflagellates (Ostreopsis cf. ovata, Prorocentrum lima and Coolia monotis) were isolated from Bizerte Bay (Tunisia, Mediterranean) and monoclonal cultures established. The ribotyping confirmed the morphological identification of the three species. Maximum growth rates were 0.59 +/- 0.08 d(-1) for O. cf. ovata, 0.35 +/- 0.01 d(-1) for C. monotis and 0.33 +/- 0.04 d(-1) for P. lima. Toxin analyses revealed the presence of ovatoxin-a and ovatoxin-b in O. cf. ovata cells. Okadaic acid and dinophysistoxin-1 were detected in P. lima cultures. For C. monotis, a chromatographic peak at 5.6 min with a mass m/z = 1061.768 was observed, but did not correspond to a mono-sulfated analogue of the yessotoxin. A comparison of the toxicity and growth characteristics of these dinoflagellates, distributed worldwide, is proposed.
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Caruana, A. M. N., Le Gac, M., Herve, F., Rovillon, G. - A., Geffroy, S., Malo, F., et al. (2020). Alexandrium pacificum and Alexandrium minutum: Harmful or environmentally friendly? Mar. Environ. Res., 160, 105014.
Résumé: Alexandrium minutum and Alexandrium pacificum are representatives of the dinoflagellate genus that regularly proliferate on the French coasts and other global coastlines. These harmful species may threaten shellfish harvest and human health due to their ability to synthesize neurotoxic alkaloids of the saxitoxin group. However, some dinoflagellates such as A. minutum, and as reported here A. pacificum as well, may also have a beneficial impact on the environment by producing dimethylsulfoniopropionate-DMSP, the precursor of dimethylsulfur-DMS and sulfate aerosols involved in climate balance. However, environmental conditions might influence Alexandrium physiology towards the production of harmful or environmentally friendly compounds. After assessing the influence of two salinity regimes (33 and 38) relative to each species origin (Atlantic French coast and Mediterranean Lagoon respectively), it appears that DMSP and toxin content was variable between the three experimented strains and that higher salinity disadvantages toxin production and tends to favor the production of the osmolytes DMSP and glycine betaine. Hence, this key metabolite production is strain and species-dependent and is influenced by environmental conditions of salinity which in turn, can diversely affect the environment. Widespread coastal blooms of A. minutum and A. pacificum, although being a risk for seafood contamination with toxins, are also a DMSP and DMS source that potentially contribute to the ecosystem structuration and climate. Regarding recent advances in DMSP biosynthesis pathway, 3 dsyB homologs were found in A. minutum but no homolog of the diatom sequence TpMMT.
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Grzebyk, D., Audic, S., Lasserre, B., Abadie, E., de Vargas, C., & Bec, B. (2017). Insights into the harmful algal flora in northwestern Mediterranean coastal lagoons revealed by pyrosequencing metabarcodes of the 28S rRNA gene. Harmful Algae, 68, 1–16.
Résumé: This study investigated the genetic diversity of phytoplankton communities in six shallow lagoons located on the French coast of the northwestern Mediterranean Sea that represented a trophic gradient ranging from oligotrophic to hypereutrophic. The phytoplankton communities were sampled once a month from spring (May) to the beginning of autumn (September/early October) in 2012 and fractionated by size. Metabarcodes were generated from cDNAs by targeting the D1-D2 region of the 28S rRNA gene and pyrosequenced using Roche 454 technology. Examination of the annotated barcodes revealed harmful algal species not previously documented in these lagoons. Three ichthyotoxic species belonging to Pfiesteriaceae were detected: Luciella masanensis was relatively widespread and abundant in many samples, whereas Pfiesteria piscicida and Stoeckeria changwonensis were found as single barcode sequences. Furthermore, a phylogenetic analysis of barcodes annotated as belonging to Pfiesteriaceae suggested the existence of two previously undescribed clades. The other toxic or potentially harmful dinoflagellates detected through rare barcodes were Dinophysis acuminata, Vulcanodinium rugosum, Alexandrium andersonii and A. ostenfeldii. The two most abundant dinoflagellate taxa were Gymnodinium litoralis and Akashiwo sanguinea with respect to sequence numbers. Four diatom species from the genus Pseudo-nitzschia that potentially produce domoic acid were identified (P. galaxiae, P. delicatissima, P. brasiliana and P. calliantha). These observations are discussed in terms of the literature and monitoring records related to the identified taxa in this Mediterranean area. (C) 2017 Elsevier B.V. All rights reserved.
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Hadjadji, I., Masseret, E., Plisson, B., Laabir, M., Cecchi, P., & Collos, Y. (2012). Clonal variation in physiological parameters of Alexandrium tamarense: implications for biological invasions and maintenance. Cah. Biol. Mar., 53(3), 357–363.
Résumé: The study of the intraspecific variability is a crucial step for understanding the successful establishment and maintenance of invasive species. Alexandrium tamarense strains isolated in spring 2007 from a single bloom in Thau lagoon have been grown on three different media (ESNW based on natural seawater, and the artificial media, ESAW, ESAW+HA). A large diversity in the ability of strains to grow on these media was found. Irrespective of medium composition, growth curves followed three models: (1) a classical shape, (2) a population crash followed in some cases (3) by growth recovery. Some strains were able to show significant growth in an environment completely artificial (ESAW). ANOVA indicated a significant difference between groups in growth rates allowing the distinction of contrasted categories among the strains studied in ESNW medium. These statistical tests also indicated the presence of distinct groups among the strains grown in the ESAW as well as for those on ESAW+HA medium. Lag phases were extremely variable between strains in all environments, suggesting a high variability of adaptation to the environment. The results revealed that wide fitness variations were exhibited by diverse conspecific A. tamarense individuals co-existing during a bloom.
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Laanaia, N., Vaquer, A., Fiandrino, A., Genovesi, B., Pastoureaud, A., Cecchi, P., Collos, Y. (2013). Wind and temperature controls on Alexandrium blooms (2000-2007) in Thau Lagoon (Western Mediterranean). Harmful Algae, 28, 31–36.
Résumé: Since 1998, blooms of Alexandrium catenella/tamarense in the lagoon of Thau developed regularly each autumn, reaching a maximum of several millions cells per liter in 2004. By contrast, spring blooms occurred only twice (in 2000 and 2007). During these periods, sea surface temperatures (SST) and the wind patterns appear to impact the bloom occurrences much more than the apparent limiting resources such as inorganic nutrients. The analysis of SST and wind from April to June and September to November (from 2000 to 2007) indicates first that there has to be an initial wind stress in order to resuspend the cysts buried in the sediment. Blooms then occur after a period of weak winds (<4 m s(-1)) and of stable SST close to 20 degrees C (+/- 2 degrees C). Those conditions appear to be most favorable for germination of Alexandrium cysts and its ensuing vegetative growth. This period of stability (a few days to a few weeks) allows the development of the inoculum from the cyst's germination, its cohesion because of reduced hydrodynamics, and development of vegetative cells that are sensitive to agitation. Strong winds during 1-2 day periods can interrupt the bloom dynamics by dispersing (advection due to southeasterly winds) and/or eliminating (turbulence due to northwesterly winds) the vegetative cells. In the spring, under the same conditions of optimal SST, strong wind episodes dominate and those, as well as biological factors very likely lead to a lower occurrence of blooms relative to the fall situation. (C) 2013 Elsevier B.V. All rights reserved.
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